Process for the production of ceramic-metal compound joints

ABSTRACT

A process for brazing a metal element having a tubular skirt to the exterior of a ceramic tube utilizes an auxiliary ring of material having the same thermal expansion characteristics as the ceramic tube placed over the skirt of the metal element during brazing.

United States Patent [191 Ebendt [451 NW. 26, revs PROCESS FOR THE PRODUCTION OF CERAMlC-METAL COMPOUND JOINTS [75] Inventor: Volker Ebendt,

Mannheim-Seekenheim, Germany [73] Assignee: Deutsche Steinzeug-und Kunstsofiwareniabrik, Mannheim, Germany [22] Filed: Dec. 14, 1971 [21] Appl. No.: 207,844

[30] Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS 1,810,998 10/1969 Germany 29/479 239,774 7/1969 U.S.S.R "29/4731 Primary Examiner-.1. Spencer Overholser Assistant ExaminerRonald J. Shore AttorneyGeorge H. Mitchell, Jr.

[57 ABSTRACT A process for brazing a metal element having a tubular skirt to the exterior of a ceramic tube utilizes an auxiliary ring of material having the same thermal expansion characteristics as the ceramic tube placed over the skirt of the metal element during brazing.

8 Claims, 3 Drawing Figures Dec. 16, 1970 Germany P 20 61 879.5

[52] US. Cl 29/473.1, 29/474.4, 29/493, 287/189.365 [51] Int. Cl. B23k 31/02 [58] Field Of Search 29/473.1, 479, 493, 29/522, 523, 474.4, 474.5, 474.6; 287/l89.365

[56 References Cited UNITED STATES PATENTS 1,940,870 12/1933 Litton 287/189.365 X PROCESS FOR THE PRODUCTION OF CERAMIC-METAL COMPOUND JOINTS The invention relates to a process for making ceramic-metal compound joints, whereby the metallic element is a highly ductile metal or a highly ductile metal alloy, which is disposed outside on the ceramic element to encase it. As such metals, preferably copper, silver and gold and their alloys are to be considered.

Ceramic-metal compound joints, or connections, have been known for a long time. At the same time the following arrangements between ceramic and metal elements constitute the status of the prior art:

1. The metal envelops the ceramic on the outside. For this type of joint, which is the most reliable one, heretofore only metals were considered whose thermal expansion coefficient was largely adapted to the thermal expansion coefficient of the ceramic. In the case of use of A1 oxide ceramic (expansion coefficient at 20 to 800 C, approximately 7 X 10 per degree C) as a raw material for the ceramic element, these metals are essentially iron-nickel and iron-nickel-cobalt alloys with a Curie temperature in the range of 300 600 C, as well as titanium and a few others as refractory metals. Their expansion coefficient at 20 to 800 C lies between and 9.5 X 10 per degree C.

By adaptation of the expansion coefficients between ceramic and metal, whenever metals and ceramic overlap compactly at ambient temperature, after heating to brazing temperature and in case the actual brazing temperature is reached, a sufficiently small air gap will be produced between the ceramic and the metal parts such that the solder will be sucked in through capillary forces. Moreover, by proper adaptation of the expansion coefficients between ceramics and metal during cooling of the brazing temperature, too high mechanical stresses of the metal on the ceramic will be avoided. In the case of outside brazing considered heretofore, these stresses are probably quite considerable because of the high degree of pressure resistance of the ceramics and they contibute to a certain extent to the strength of the metal-ceramics compound.

2. The ceramic element envelops the metal on the outside, the metal fitting against the inside cylinder wall of an aperture of the ceramic element. In the case of a small diameter hole, this ceramics-metal compound connection can be realized by means of the metals mentioned in the foregoing paragraph. It furthermore has been known in the case of small diameters to use nickel for this purpose in the form of a tube. As stated previously, such joints however are possible only for relatively small diameters up to about 2 mm inside width of the hole, since otherwise during cooling of the brazing temperature the differences in dimensions occurring between the metal and the ceramic element will lead to such high stresses that the brazed layer or the ceramics will crack.

Conditions are somewhat more favorable when highly ductile metals, such as copper, silver or gold free of oxygen are used for this type of compound joint. These metals, of course, have a larger difference in thermal expansion with reference to the ceramics than the previously mentioned ones (expansion coefficient at 20 C to 800 C is above X 10' per degree C), however in these metals the stresses occurring during cooling down from the brazing temperature can be largely reduced by plastic flow.

It therefore is possible with this technique to close relatively large apertures of more than 20 mm inside width by copper brazings as long as care is taken to keep the copper sufficiently thin, perhaps not thicker than 0.5 mm. so that the resulting forces will remain small.

3. Flat brazings also are possible where metallic foils are soldered, for example, onto the front side of ceramic rings, and thus the inside opening of these rings is covered up. In this case too, the use of thinwalled and ductile metals, such as copper, silver and gold, is advantageous.

However, heretofore it was not possible to braze metals with thermal coefficients deviating considerably from the ceramics directly on the outside onto the ceramics in an enveloping manner. Whenever such joints were desired, it was necessary to produce the ceramics and the metal connection by way of expensive intermediate solutions. A typical construction of this type consists, for example, in that a part made of one of the above mentioned metals, adapted with regard to its expansion coefficient to the ceramic, is soldered on the outside in an enveloping way to the ceramic element and the desired copper flange will be soldered only to this metal element. Therefore, two soldered seams were necessary with an intermediate part made of some other metal, in order to produce the connection be tween copper and a ceramic element.

Now the process according to the present invention creates the possibility of a ceramics-metal compound joint even for parts made of metals whose expansion coefficient deviates greatly from that of the ceramic element and where the metal element envelops the ceramic element from the outside whenever the metal used is ductile. The essential inventive idea is to be explained in more detail on the basis of the drawings, in which FIG. 1 is an axial cross-section of a preferred form of ceramic-metal joint in accordance with the invention, and FIGS. 2 and 3 are similar views of modified forms.

In FIG. 1, reference number 1 designates a ring made of ceramic material, 2 is a metal element made of a ductile metal, for example copper, silver or gold, or a ductile alloy, and 3 designates an auxiliary ring made of the same ceramic material from which ring 1 is made.

FIGS. 2 and 3 show some other embodiments of the inventive idea. In these figures, reference number 4 is the ceramic element of the compound construction, 5 and 6 are flanges disposed according to the invention and 7 and 8 are auxiliary rings of the same material as ceramic ring 4. In FIG. 3, reference number 9, designates the ceramic element of the metal-ceramics compound construction, 10 and 11 designate the metal elements designed according to the invention and 12 the auxiliary ring made of the same material as ceramic ring 9.

In order to achieve the metal-ceramics compound joint with an outside enveloping metal element made of a highly ductile metal, the metal element is slid with a tight fit, that is to say a clearance up to about 0.05 mm. over the ceramic element, with which it is to be connected. Naturally, the ceramic element at those places where the brazing connection is to be made must carry a corresponding known metal layer. It can consist, for example, of a basic metallic coating of molybdenummanganese, constituting part of the status of the prior art, with a galvanically applied nickel layer. Then an additional ceramic ring will be placed invertedly over the metal element, the inside width of which ring must be fitted very tightly to the outside diameter of the metal part. In this case too a clearance of 0.05 mm or less has proven to be advantageous.

Such an arrangement is shown in FIG. 1, the actual metal-ceramic compound joint consisting of the ceramic ring 1 and the metal part 2. The brazing is accomplished along the contact surface between these two parts. The auxiliary ring has the number 3 and encircles the metal element 2. Similarly, the compound joint of FIG. 2 consists of ceramic ring 4 and the two metal parts 5 and 6 with the two auxiliary rings 7 and 8, whereby the auxiliary ring 7 closely envelops the metal part 5 and auxiliary ring 8 the metal part 6. In FIG. 3 the actual ceramic-metal compound joint consists of ceramic ring 9 and metal parts 10 and 11, which in this case are surrounded by the common auxiliary ring 12.

The arrangements described in the preceding paragraph are joined together at ambient temperature and heated to brazing temperature. At the same time the ceramic elements which comprise the actual compound joint (I, 4 and 9) and the auxiliary rings (3, 7, 8 and I2) always expand evenly, since they consist of the same ceramic raw materials. As mentioned previously, the metal parts 2, 5, 6, l0 and 11 have a considcrably higher expansion coefficient compared to that of the ceramics. If auxiliary rings 3, 7, 8 and 12 were not present, then these metal parts during heating to brazing temperature would expand so far that, during the brazing temperature, there would be a considerably larger brazing gap, so that reliable and precise brazing would not be possible. The metal parts are impeded in their thermal expansion by auxiliary rings 3, 7, 8 and 12, whereby the thermal stresses developing during the process of restraint can be reduced, since these metal elements consist of ductile raw materials.

Upon reaching the brazing temperature therefor, a narrow brazing gap favorable for brazing will be provided between the ceramic elements of the compound joint and the metal parts. The filler material can be sucked into the brazing gap and can solidify in the brazing gap in a sufficiently thin layer during cooling. The mechanical stresses developing during cooling from the brazing temperature to ambient temperature can again be reduced in the metal element by way of plastic flow and therefore will not lead to fissures.

It is possible with the process described to produce highly vacuum tight connections between mechanically highly refractory ceramic elements and metal compound joints with metal parts made of copper, silver and gold or highly ductile alloys enveloping the ceramics on the outside in a reliable manner.

I claim:

1. Process for the production of ceramic-metal compound joints of the type wherein a first element of ceramic material has an exterior peripheral surface, comprising the steps of placing a second element composed ofa ductile metal having a skirt in position for the skirt to encircle said peripheral surface with a tight fit at ambient temperature, placing an auxiliary element composed of a material having a thermal coefficient of expansion similar to that of the first ceramic element and having an internal surface corresponding to the exterior of the skirt of the second element in position for the internal surface to encircle the skirt with a clearance no greater than 0.05 mm at ambient temperature, and brazing said second element only to said first element.

2. Process defined in claim 1, which includes the step of heating said elements to a temperature sufficient to induce a brazing material to enter the gap between the first and second elements by capillary attraction.

3. Process defined in claim 2, which includes the step of introducing said brazing material to said gap while said elements are at a temperature above ambient.

4. Process defined in claim 3, wherein said auxiliary element comprises a ceramic material having a com position similar to that of said first ceramic element.

5. Process defined in claim 4, wherein said first and auxiliary elements comprise oxide ceramics having the composition A1 0 6. Process defined in claim 4, wherein said second element comprises a metal alloy having a thermal expansion rate at 20 C. to 800 C. greater than 15 X 10 per degree C.

7. Process defined in claim 4, wherein said second element comprises one of the metals gold, silver and copper.

8. Process defined in claim 7, wherein said first and auxiliary elements comprise oxide ceramics having the composition M 0 

1. Process for the production of ceramic-metal compound joints of the type wherein a first element of ceramic material has an exterior peripheral surface, comprising the steps of placing a second element composed of a ductile metal having a skirt in position for the skirt to encircle said peripheral surface with a tight fit at ambient temperature, placing an auxiliary element composed of a material having a thermal coefficient of expansion similar to that of the first ceramic element and having an internal surface corresponding to the exterior of the skirt of the second element in position for the internal surface to encircle the skirt with a clearance no greater than 0.05 mm at ambient temperature, and brazing said second element only to said first element.
 2. Process defined in claim 1, which includes the step of heating said elements to a temperature sufficient to induce a brazing material to enter the gap between the first and second elements by capillary attraction.
 3. Process defined in claim 2, which includes the step of introducing said brazing materiAl to said gap while said elements are at a temperature above ambient.
 4. Process defined in claim 3, wherein said auxiliary element comprises a ceramic material having a composition similar to that of said first ceramic element.
 5. Process defined in claim 4, wherein said first and auxiliary elements comprise oxide ceramics having the composition Al2O3.
 6. Process defined in claim 4, wherein said second element comprises a metal alloy having a thermal expansion rate at 20* C. to 800* C. greater than 15 X 10 6 per degree C.
 7. Process defined in claim 4, wherein said second element comprises one of the metals gold, silver and copper.
 8. Process defined in claim 7, wherein said first and auxiliary elements comprise oxide ceramics having the composition Al2O3. 